1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a method for fabricating a liquid crystal display (LCD) panel by a liquid crystal dropping method.
2. Discussion of the Related Art
A thin flat panel display tends to have a thickness of no more than a few centimeters. Particularly, a liquid crystal display (LCD) has a wide scope of applications, such as notebook computers, computer monitors, gauge monitors for space crafts, and air crafts, and the like.
In general, the LCD is provided with a lower substrate having thin film transistors and pixel electrodes formed thereon, an upper substrate opposite to the lower substrate having a black matrix (BM), a color filter layer, and a common electrode, which are formed thereon, and a liquid crystal layer between the two substrates, for driving the liquid crystal by the electric field generated by the power supply applied to the pixel electrode and the common electrode between the substrates, to regulate the transitivity of the liquid crystal, thereby displaying a picture on the display screen.
In the foregoing LCD, a vacuum injection method has been used for forming the liquid crystal layer between the lower substrate and the upper substrate. In such a method, after the lower substrate and the upper substrate are bonded together, a liquid crystal is injected between the two substrates by using capillary phenomenon and a pressure difference. However, the vacuum injection method takes much time to inject the liquid crystal between the substrates. As a result, productivity is much reduced as the substrate becomes large.
Consequently, a method called a liquid crystal dropping method is suggested for solving such a problem. A method for fabricating an LCD panel by using a related art liquid crystal dropping method will be explained with reference to the attached drawings.
FIGS. 1A to 1E illustrate expanded perspective views showing a method for fabricating an LCD panel by using a related art liquid crystal dropping method. For convenience, only four unit cells are illustrated in the drawings.
Referring to FIG. 1A, a lower substrate 1 and an upper substrate 3 are prepared for the process. A plurality of gate lines and data lines (both not shown) are formed on the lower substrate 1 to cross each other defining pixel regions. A thin film transistor is formed at every crossing point of the gate lines and the data lines. A pixel electrode is formed at every pixel region connected to the thin film transistor.
A black matrix is formed on the upper substrate 3 for shielding a light leakage from the gate lines, the data lines, and the thin film transistor regions. A color filter layer of red, green, and blue is formed thereon. A common electrode is formed thereon in this order. An orientation film is formed on both of the lower substrate 1 and the upper substrate 3 for an initial orientation of the liquid crystal.
In FIG. 1B, a main sealant 7 and a dummy sealant 8 are coated on the lower substrate 1, and a plurality of liquid crystal droplets 5 are positioned thereon to form a liquid crystal layer. Then, spacers (not shown) are spread on the upper substrate 3 for maintaining a cell gap.
The main sealant 7 prevents the liquid crystal from leaking, and bonds the upper and lower substrates. The dummy sealant 8 is formed at the dummy region on the outside of the main sealant 7. The dummy sealant is to protect the main sealant 7.
In the liquid crystal dropping method, the liquid crystal layer is placed between the attached substrates before hardening a sealant. Accordingly, if a thermo-hardening sealant is used to bond the substrates, it may flow and contaminate the liquid crystal during the heating process. Thus, a UV sealant has to be used as a sealant to avoid such a problem.
Referring to FIG. 1C, the lower substrate 1 and the upper substrate 3 are attached to each other. As shown in FIG. 1D, a UV ray is irradiated by using a UV irradiating device 9, to harden the sealant 7 (shown in FIG. 1B), thereby bonding the lower substrate 1 and the upper substrate 3. FIG. 1E illustrates the bonded substrates 1 and 3 are cut into a plurality of unit cells.
FIG. 2 illustrates a process for cutting the substrates into the unit cells. In FIG. 2, a scribing line is formed on the surface of the bonded substrates 1 and 3 using a scriber, such as a diamond pen having a hardness greater than glass, which is a material of the substrates (scribing process). Thereafter, a mechanical impact is given along the scribing line 10 (break process), to cut into a plurality of unit cells. Alternatively, a diamond pen or wheel may be used, to carry out the scribing process and the breaking process in one process, to obtain the unit cell one by one.
FIG. 2 is provided for illustrating the cell cutting process, and the scribing line is not shown in detail. More scribing lines may be formed to remove the dummy region at the outside of the cell in the actual cell cutting process.
FIG. 3 illustrates a plane view of the scribing lines in detail. Particularly, sealants 7 and 8 formed on the lower substrate 1 are illustrated with the scribing lines 10.
Referring to FIG. 3, the scribing line 10 overlaps a portion of the dummy sealant 8 at the region (shown as circles) when the dummy sealant 8 is hardened by the UV irradiating process before the cell cutting process.
Consequently, unit cells the hardened dummy sealant 8 does not cause a problem when the scribing and breaking are processed one by one to obtain unit cells. However, when unit cell one by one by the scribing and breaking are processed at the same time, it will be difficult to cut into the unit cell due to the hardened dummy sealant 8.